Chromatography



July 11, 1961 Filed July 12, 1957 CARRIER GAS & 1

R. J. HARRIS CHROMATOGRAPHY 4 Sheets-Sheet 1 DETECTOR- HEATED CHAMBERCHROMATOGRAPHIC COLUMN FIGURE I SAMPLE INLET SYST E CARRIER GAS Rono J.Harris Inventor R. J. HARRIS CHROMATOGRAPHY July 11, 1961 4 Sheets$heet2 Filed July 12, 1957 Runo J. Harris Inventor 4 Sheets-Sheet 3 R. J.HARRIS CHROMATOGRAPHY Mm mm 1% 511 I r 2 H mmDwE July 11, 1961 FiledJuly 12, 1957 Runo J. Harris Inventor July 11, 1961 R. J. HARRIS2,991,647

CHROMATOGRAPHY Filed July 12, 1957 4 Sheets-Sheet 4 FIGURE I Rono J.Harris Inventor samples into the apparatus. 1 the sample also must betaken into account.

2,991,647 CHROMATOGRAPHY Rano Joseph Harris, Baton Rouge, La., assignorto Precision Instruments Company, a partnership in Louisiana Filed July12, 1957, Ser. No. 671,573 3 Claims. (Cl. 73-23) The present inventionrelates to gas chromatography. It more particularly relates to a methodand means for quickly and reproducibly injecting small samples intovapor-liquid partition adsorption chromatographic apparatus. V

In brief compass, this invention proposes an improved method forintroducing exceedingly small liquid or gaseous samples into a carriergas as used in chromatographic analysis. This improved method comprisesflowing the carrier or eluting medium at a uniform rate through apassageway past an orifice or seating means and into a chromatographiccolumn used for resolving the sample, and introducing the sample bymeans of a small capillary pipet into the carrier medium through theagency of the orifice. One end of the small capillary pipet matches andregisters with the orifice in the passageway. The pipet contains asample containing capillary bore, one end of which opens on the end ofthe pipet that matches with the orifice. The other end of the bore openson the side of the pipet or other end. Thus, when the pipet is contactWith the orifice, the eluting or carrier medium flows through the bore,purging it of its contents. Shortly after this, the pipet is withdrawnto permit continued passage of the carrier medium through the orificeinto the column.

As it is known in the art in gas chromatography, small samples-usually0.0001 to 1.0 ml. for liquids and 0.01 to 100 ml. of gases-mustinstantly and reproducibly be injected into the carrying fluid thattransports the sample through the chromatographic column whereinresolution of the sample is attained. Besides the exceedingly smallvolumes involved, the fact that the flow of the carrying fluid must besubstantially uniform and that the fluid is under pressure, furthercomplicates injection of The volatility or viscosity of The presentinvention proposes a versatile method and apparatus for satisfactorilyintroducing samples, both liquid and gaseous, into chromatographicapparatus. This new method gives excellent reproducibility withessential- 1y no time lag and consequent loss in column resolution.

This invention will become clear from the following description of thedrawing attached to and forming a part of this specification.

In the drawings, FIGURE I illustrates one type of chromatographicapparatus to which the sample inlet system of this invention isapplicable;

FIGURE II illustrates one preferred embodiment of the sample inletsystem of this invention;

FIGURE III illustrates one type of pipet assembly adapted to handleliquids;

FIGURE IV illustrates one type of pipet assembly adapted to handlegases; and

FIGURE V illustrates some modifications of the apparatus of thisinvention.

Referring now to FIGURE I, illustrated is a chromatographic column =1filled with an adsorptive solid or, as in this example, an inert,relatively porous packing, such as crushed firebrick 2. Carried on thisfirebrick is an absorbent material, usually a high molecular weightliquid such as an oil or soap, e.g., a heavy lubricating oil. A carrierfluid supplied by line 3 is admitted to the inlet of column 1. Thiscarrier fluid is preferably first passed through the detection means 6by line 8 so that a simple differential analysis can be made. For thepurpose of this example of vapor-liquid partition chromatography, thefluid is helium although equivalent gases, such as nitrogen, can beused. It is important, in order to obtain reproducible results, that theflow of the carrier fluid through the column be substantially uniformand constant.

The whole of the system so far described is maintained within a furnaceor other similarly heated chamber 5, so that a substantially uniformtemperature can be maintained. The temperature used generally is in therange from 0 to 600 F. The helium gas, in passing through coil 3a, isheated up to the operating temperature.

In general, this type of chromatographic apparatus operates by injectionof a small sample-say, a mixture of C to C hydrocarbons-into the carrierfluid, as by line 9. The sample can be heated at the point of injectionto assist the rapid vaporization of higher boiling materials. Thehydrocarbon components of the sample are then carried through thecolumn, being picked up in part by the absorbent and then beingdeabsorbed at different time intervals, whereby they are separated orresolved. Some time after injection of the sample, say 1 to 30 minutes,the first component of the sample appears in the gases emerging from thecolumn and its presence is detected in the helium gas by a detector 6,and each component-as it appears in the exit gas-is similarly detected.After having passed through the detection apparatus, the gases can bevented by line 7 or collected as desired.

The sample, in passing through the column, is resolved because of thedifferences in the vapor-liquid equilibria for each component of thesample with respect to the absorbent in the column. These differentcomponents of a sample emerge at different characteristic times for agiven set of operating conditions.

Detector 6 is used to measure some physical characteristic of the gas,such as thermal conductivity, density, charged particle ionizationcharacteristics, infra red radiation absorption, etc. It is customary tomeasure the characteristic of the exit gas relative to the incomingcarrier gas to obtain a more accurate and simpler analysis. The detectorcan consist, for example, of a means of measuring the thermalconductivity of the exit gas rela tive to that of the incoming carriergas. Thus, as the different components of the sample appear in the exithelium carrier gas, the thermal conductivity will change. The identityof a compound in the sample causing a change in thermal conductivity isobtained by calibration of the apparatus with respect to time. For agiven set of operating conditions, any single compound will have acharacteristic time of appearance in the exit carrier gas relative tothe time of injection of the sample. This information, e.g., change inthermal conductivity, ob tained by detector'6 is customarily plottedagainst time. The amount of the compound in the sample can then bedetermined from the height or magnitude in the change recorded by thedetector, or more properly can be obtained by the area under the curvecaused by the compound.

The above description is intended to be only exemplary of apparatus towhich the improvement of this invention is applicable. Similar apparatuscan, of course, be used.

The improvement of this invention relates to the manner of introducingthe small sample into the system. The sample inlet system of thisinvention as shown in FIG- URE I, is to the right of connection 4connecting the inlet system to the initial portion of thechromatographic column, indicated generally as line 9.

Referring to FIGURE II, this inlet system comprises in one embodiment aninlet conduit 11 connecting with connection 4, into which the helium gasin line 3a is introduced. An orifice or seating arrangement 10 is placedwithin conduit 11 downstream of the point of carrier gas admission.Orifice I10 is here shown as being integral with connection 4, but thisis not necessary. Orifice 10 can be made of yielding rubber, Teflon (Du-Pont trademark for fluorine containing ethylene resin), or similarplastic. For high temperature service, brass, stainless steel, orsimilar metals can be used. Conduit 11 terminates in a valve 14 of thestopcock or plug valve type that, when open, permits passage of a rod ortube into conduit 11, as explained below. Another conduit 15, extendingfrom the other side of valve 14, terminates in a sealing means 16 which,in this case, comprises an ring seal 17. A bracket 12 is used to attachthe inlet system to the cabinet containing the chromatographic column,the bracket also supporting valve 14 by bolt 13.

In normal operation valve 14 is closed and helium from line 3continuously flows at a uniform rate in line 11, through orifice 10, andinto colum 1.

The sample carrier of this invention, shown in FIG- URE III, comprises asmall pipet 29 which has a small capillary bore 18. The end of thispipet registers or matches with orifice 10, and is preferably precisionshaped or ground to a taper angle of 15 to 45". As shown in theenlargement, it is especially preferred to give the tip of the pipet anadditional taper to aid in guiding it into the orifice. The fit of thepipet with the orifice is such that the shoulder of the orifice, whichneed not be knife-edged as shown, evenly circumferentially contacts thetaper of the pipet. A suitable orifice of another type can comprise aplastic O-ring held in place by a ring retainer in coupling 4. Theupstream side of orifice can also be tapered as illustrated to aid inguiding the pipet. One end of the capillary bore 18 terminates in theend of the capillary pipet that registers with the orifice, so that thebore is aligned to discharge its con- ,tents on the other side of theorifice. The other end of the capillary bore is exposed to the carrierfluid or gas in line 11, supplied by line 3a.

In a much preferred embodiment of this invention, the capillary bore ofthe pipet is specially made such that the ends are of smaller diameteror cross-sectional area than the central section. This is to preventundue loss of the sample, especially with gaseous or volatile liquids.With a liquid handling pipet, the diameter of the inlet to bore is inthe order of 0.05 to 0.5 mm., and the diameter in the middle is in theorder of 0.1 to 5.0 mm. For gases, the inlet to the bore is in the orderof 0.05 to 1.0 mm. in diameter, and the middle of the bore can be up to5.0 mm. or more in diameter, so long as piston fiow is achieved duringdischarge of the sample. The capacity of the pipet for liquid samples ispreferably in the range of 0.0001 to 1.0 ml. The capacity for gassamples is substantially larger and is preferably in the range of .01 to100 ml. For ease of cleaning, and to permit observation of the sample,the smaller pipets for liquids are preferably made of glass, althoughthey can be made of metal or other suitable materials. The larger metalpipets for gas samples are preferably made of stainless steel to avoidcontamination problems.

The bore of the pipet, While it can run longitudinally through thepipet, is preferably turned as shown to emerge on the side of the pipet.This permits convenient in line attachment of a handle 19 to the pipet.

The pipet can be loaded in several ways. One way, when handling liquid,is simply to insert the end of it in the liquid and allow capillaryaction to draw in the sample. It can be purged, when handling gases,with the desired gas to be filled. Alternatively, a hypodermic needle oraspirator bulb can be used to fill the capillary bore.

Th capillary pipet carrying the sample is inserted into the sample inletsystem by inserting pipet 20 through sealing means 17, up to valve 14which is closed. It is preferred to purge line before insertion of thepipet as by bleeding carrier gas through valve 14, or by means of apurge line 22, shown in FIGURE II. Valve 14 can also be a 3-way valve orcan be drilled to permit passage of purge gas to line 15.

Pipet 20 is of smaller diameter, preferably, than handle 19. The 0 ringseal 17 mates with handle 19, and provides a firm fit. In some cases thecolumn may be operated under pressure as high as 50 psi. or more, andthe design of sealing means 1 6 is sufficient to prevent any appreciableloss of gas. A mark can be placed on handle 19 to tell when the pipet isapproaching valve 14. After handle 19 makes a seal with 0 ring seal 17,valve 14 is opened and the passage of the pipet is continued untilcontact is made with orifice 10.

Upon contact with orifice 10, the contents of pipet 20 are dischargedbecause the flow of the carrying fluid is temporarily interrupted andthus forced through capillary bore 18, expelling or purging it of itscontents. Within a few seconds, e.g., l-20, depending on the size of thepipet, the pipet is Withdrawn to allow continued passage of the carryingfluid without substantial interruption.

The pipet shown in FIGURE III is designed primarily for liquids. Toaccommodate gases, the capillary bore can simply be expanded but thismay be disadvantageous for large gas samples, i.e., greater than 1 00.,in that nonpiston flow may attain and thus result in an appreciable timelag in purging the bore. For this reason, when it is necessary to handlea large volume of gas, the apparatus of FIGURE IV may be preferred. Inthis arrangement, a pipet 30 contains what might be termed a capillarytube 31. For example, this may comprise small bore steel tubing, e.g.,0.01 to 0.25 inch I.D., such as used in hypodermic needles. This tubeextends from the end of the pipet that registers with the orifice,through the opposite end of handle 32, and is curved or coiled at 33 toprovide the requisite volume. The other end of the capillary tube isthen passed back Within to the pipet, and emerges through the side wallof the pipet at 34. As an example, pipet 30 can have an outside diameterof i -inch, and the handle can have a diameter of about fit-illch. Thecapillary tube can have a bore of A -inch and an overall length of 6feet. It is convenient to provide quick couplings or connectors 35 ontubing 31 as shown, to permit ready attachment of coils of differentsizes to the pipet, and thus to permit ready adustment of the capacityof the gas pipet. Also, it is convenient to incorporate coil 33 in anenlarged handle, not illustrated, attached to handle 32, to permiteasier handling of the pipet.

In one particularly preferred embodiment of this invention, the externalsurface of the pipet handle 19 (See FIGURE III) is Teflon, or similarplastic. The lubricity of Teflon permits smooth insertion of the pipetinto the sample inlet system. For example, handle 19 can be coated withTeflon, or can be entirely made of Teflon with pipet 20 fitting thereinby a press fit, as shown. The latter construction is advantageous whenglass pipets are used because it gives some flexibility to the pipetassembly.

The lubricating characteristics of Teflon can also be used to advantagein valve 14. It is preferred to form the rotating plug of the valve fromTeflon to eliminate the need for a lubricating grease which might causesample contamination.

In FIGURE V some modifications of the invention are shown. In FIGURE V,parts similar to those illustrated in FIGURE II bear the sameidentification numbers.

When a sample is volatile, some of the sample can be lost by prematurevolatilization of the sample. This can be satisfactorily overcome byprecooling of the pipet and/or sample. For example, the pipet can beimmersed in liquid nitrogen before, and after, if desired, the sample isplaced in the pipet.

With viscous and relatively non-volatile samples, it is desirable tosupply heat to the pipet to permit removal of the sample by the carriergas. Otherwise, substantially instantaneous introduction of the samplemight not be attained, and the results might not be as accurate asdesired, e.g., peak heights for the individual components may beaffected. This heating can be done by externally heating the sample, butthis can result in premature volatilization and partial loss of thesample.

As illustrated in FIGURE V, one means of heating the pipet at the pointof introduction, is to externally heat orifice 10, as by heating coils50, which can comprise, for example, an electric heating tape. Toenhance the rapid heating of the sample, a heating and dispersing means51 can also be placed behind the orifice, usch as a metal frit, severallayers of fine screen, etc. This can be yieldingly held in place by aspring 52 which permits the end of the pipet to contact means 51 withoutdanger of breakage.

When the chromatographic column is running at a relatively hightemperature, or when heating means 50 is used, it may be desirable toprevent the transfer of heat by pipe 11 outwards to valve 14, forexample, to protect plastic parts or lubricant in the valve, and toprevent premature volatilization of liquid samples. This can be done bywrapping a cooling coil about pipe 11, or, as illustrated for theparticular arrangement shown, by attaching cooling fins 55 to pipe 11.

As an example with reference to FIGURE III, a pipet adapted for liquidsamples is formed from a %;-inch 0.D. pyrex glass tube, 4- /8 incheslong. The length of the capillary bore therein is about /2 inch, and hasa capacity of 0.00159 ml. This glass tubing is supported by a handleformed from a Ai-inch O.D. Teflon rod, 7 inches long, the glass tubingfitting by a press fit 1 inch into the handle.

To test the precision of this pipet for introducing liquid samples,normal hexane was introduced twenty times via the pipet into aPerkin-Elmer Fractometer System operating at 25 p.s.i.g., with a heliumflow rate of 120 ml. per minute (at one atmosphere and roomtemperature). The column was operated at 50 C., using 10 ft. of 30%l-octadecene on No. 545 Celite. Using the measured peak heights, the 95%confidence limits for the peak heights were found to be i 0.89% of thepeak height, which is highly satisfactory.

It can be seen that this invention permits substantially instantaneousand reproducible introduction of samples of known and constant volumeinto chromatographic apparatus. Operator error is eliminated inmeasuring the samples. It is not necessary to normalize the resultsobtained by the method of this invention, which must be done with theprior art apparatus, and the system can readily be used for partialcomponent analysis.

Further descriptions and examples of this invention can be found in thefollowing articles:

Sample Introduction System for Gas Chromatography, Tenney and Harris,Analytical Chemistry, vol. 29, No. 2, pps. 317-318, February 1957.

"Greater Precision with the Fisher-Gulf Partitioner, The Laboratory,vol. 25, No. 4, pps. 116-117, Fisher Scientific Company, Publisher.

Having described this invention, what is sought to be protected byLetters Patent is succinctly set forth in the following claims.

What is claimed is:

1. Apparatus for chromatographic analysis which comprises achromatographic column, an inlet conduit for passing a carrying fluid tosaid column, a seating means Within said inlet conduit and a capillarypipet removably fitting with the upstream side of said seating means,said pipet comprising a small elongated rod with an open ended capillarybore, one end of which opens in the face of said pipet that registerswith said seating means and the other end of said bore opening withinsaid inlet conduit when said pipet is in contact with said seating meanswhereby, when the pipet is seated in said seating means, said carryingfluid is caused to flow through said bore and the contents of saidcapillary bore are expelled by said carrying fluid through said seatingmeans and into said column.

2. The apparatus of claim 1 wherein said inlet conduit includes inletmeans for admitting and contacting said pipet with said seating meanswhile maintaining a pressure seal, said inlet means comprising abranched conduit for introducing said carrying fluid into said inletconduit upstream of said seating means, a valve in said conduit beyondsaid branched conduit adapted to provide passage when open for saidpipet, and a sealing means beyond said valve providing a yielding fitabout the rearward portion of said pipet, and forming therewith amoderately tight seal.

3. A pipet for introducing small fluid samples into chromatographicapparatus which comprises a small elongated member having a capillarybore open at both ends, one end of said bore opening in the centralportion of one face of said elongated member, and an aligned handlesubstantially longer than said elongated member and attached to saidelongated member at the opposite end from said face, said handle beinglarger in diameter and substantially longer than said elongated memberand said here comprising capillary tubing which extends from said facethrough the other end of said elongated member and handle to a coil, theother end of said tubing returning through said handle and elongatedmember and terminating and opening on a side wall of said elongatedmember.

References Cited in the file of this patent UNITED STATES PATENTS GasChromatography II, by N. H. Ray in Journal of Applied Chemistry, vol. 4,p. 82, Feb. 1954, pp. 82-85.

Gas Chromatograph in Oil and Gas Journal, Dec. 17, 1956, pp. 126-14Book: Vapor Phase Chromatograph (Desty), Butterworth ScientificPublications, London, 1956, pages 287, 423.

